I currently use an inline reducer in my mini itx pc to run the 80mm fan at a slower speed. I'm trying to do away with as many extra cables as possible so would like to solder a resistor into the existing cable to do the same job. Anyone know what resistor I would need, I'm currently using the reducer that came with a titan fenrir.
http://www.blackfiveservices.co.uk/fanspeed.shtml Page has a calculator. not sure how what you would use to handle heat in resistor though.
Oooh very useful thanks. I should know all this seeing as I have several city and guilds certificates in electrical and electronics. (slightly embarrased )
Why not just swap the 5V and ground pins over and run the fan at 7V, no resistor required? S'what I used to do.
Another interesting bit of info, great, thanks. Think I need a new brain, normally I would think of these things myself.
Huh? I've never seen an 80mm case fan running on 5V. They're 12V (except when they're 240V/120V, which you'd certainly know about.) Running it at 7V (12V positive, 5V ground) will make it run slower, running it at 5V (5V positive, 0V ground) will either make it run really slowly or make it not run at all depending on the fan. Got a model number of the fan, or any pictures of the connector?
How do you get 7v between the 12v+ (yellow) and 5v- (black) ? On most PSUs the ground is the same for all voltages (they're all connected by a big blob of solder on the PCB)
5V isn't black; it's red. Black is 0V, or common ground. Yellow is 12V. A fan is normally wired with yellow on the positive and black on the negative, which gives you (12V-0V) 12V. Swapping the negative connection to red instead of black gives you (12V-5V) 7V. So, you can wire a fan like this: Positive Yellow, Negative Black = 12V Positive Red, Negative Black = 5V, may or may not work Positive Yellow, Negative Red = 7V, works fine Positive Black, Negative Anything = Negative or zero voltage, won't work Don't believe me? Get a multimeter, set it to DC voltage in the 0-10V range and stick the red (positive) probe in the yellow-wired pin of a four-pin Molex and the black (negative) probe in the red-wired pin. Tell me what the multimeter display sez.
Oh right! I thought you meant using the 5v rail's ground, which is just ground (rarely separate from the 12v rail's ground).
Ah, no. I mean this: (Why yes, I did dig out a power supply, switch, multimeter and camera to do that. Procrastinate, me? Never, and here's a seventeen-page essay on the reasons why not...)
It's an 80mm fan that came with my elite 120, I'll have a look at the model in a minute. It's connected via a molex to 4 pin adaptor and there is only 1 red and 1 black wire which looking at wiki the red wire in question is 5v.
The wires on the fan are not the colours you need to look at; it's the wires on the Molex. I'll bet dollars to doughnuts that the red wire on the fan side is connecting to the yellow wire on the Molex side. Either that, or you have the only 5V 80mm case fan in history. (As you're probably aware from your C&G courses, absent any other mandated colour convention red is used to indicate positive voltage and black to indicate ground. Only where multiple voltages are present would one normally use additional colours. Hence the two-wire fan has red for positive and black for ground, while the four-wire Molex has yellow for positive 12V, red for positive 5V, and black for both grounds.)
Hi Gareth. The red wire I was referring to is on the molex adaptor, the fan has a flat all black cable design with a 3 pin plug on the end which I have connected to it's mating end on the adaptor. (via the afore mentioned reducer). Made a slight error it's actually connected to 120mm bit fenix fan, the 80mm is connected to a motherboard header. I'll take a piccy of it.
move the black wire to the otherside of the molex connector and it should give you a voltage differential of 7v - one on 12v one on 5v should give you the magic 7v you want. (I think? Wait for Gareth to confirm )
Take that adapter. Plug it into a Molex connector on any power supply. Note that the red wire on the adapter is connecting to the yellow wire from the PSU. It's a 12V fan, like I said. The adapter uses red because lazy, or (as I said) there are only two wires in it and red+ black- is standard for two-wire DC. Now, remove the black wire and its pin from the four-pin Molex end of that adapter. Replace it into the spare hole on the edge of the connector, so you have the red wire where it is now, two gaps, and the black wire. Hook it up to your PSU and fan. Note the fan now spins more slowly, no resistor required. Shower me with lavish praise.
Cool thanks Gareth and Margo, that's one more adaptor disposed of(the reducer). My Elite 120 is getting roomier and roomier
